There are many well tools that incorporate a sealing member that is deformed into sealing engagement with a casing string. Typically such tools are called plugs, one species of plugs being packers. Many plugs are designed to be soluble, meltable or drillable, i.e. they incorporate a modest amount of materials that not easily drillable and are typically mostly made of composites, polymers, aluminum, brass and the like which are easily removed from a well in any of a variety of ways.
These type tools usually incorporate slips that grip the interior of a casing string, an expansion device or devices to expand the slips into gripping engagement with the casing string and a deformable or resilient seal member that is compressed during actuation of the plug so it expands more-or-less radially into sealing engagement with the casing string. An element often used in such devices is known as a back up ring, a support ring, a back up shoe, a gage ring or the like, the purpose of which is to restrain axial expansion of the deformable seal so it is directed radially against the casing string. In other words, these devices are anti-extrusion devices which minimize or prevent extrusion of the malleable seal axially along the tool and thereby minimize or prevent leakage past the seal.
Disclosures of some interest relative to this invention are found in U.S. Pat. Nos. 3,554,280; 4,397,351; 4,730,835; 5,024,270; 5,540,279; 6,739,491; 7,578,353; 8,066,065 and 8,336,616.